And I'm Steve Inskeep. Britain's Guardian newspaper has released documents that reveal more about this country's National Security Agency and its surveillance programs. The documents involve the Foreign Intelligence Surveillance Court which is supposed to oversee and give approval to surveillance programs. That's the court that meets in secret to assess requests for surveillance against suspected foreign agents. Now, the documents that have been released outline rules that the NSA says it must follow to avoid illegally targeting people in the United States. Here's NPR's Dina Temple-Raston.

DINA TEMPLE-RASTON, BYLINE: General Keith Alexander, the head of the National Security Agency, was unequivocal about who the NSA can target. He testified on Capitol Hill this week.

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GENERAL KEITH ALEXANDER: To repeat something incredibly important, the NSA is prohibited from listening to phone calls or reading emails of Americans without a court order. Period. End of story.

TEMPLE-RASTON: The two FISA documents are a total of 18 pages long and lay out procedures for handling communications. Depending on your point of view, the detail could either provide confidence that the NSA isn't trying to read your emails or make you worry that it might be. The order instructs the NSA to use all the information at its disposal to determine if it's only targeting non-United States persons.

If analysts are looking at telephone data they are supposed to look for an area code or country code to determine whether the communications came from Maryland or Morocco. If it's Maryland, they are supposed to discard the information. For emails, IP addresses that appear to be in the U.S. are also supposed to be tossed.

But there are some caveats. The NSA can keep the data - even U.S. data - for up to five years. If analysts can't easily figure out where the target is from, they can read the content of an email to look for clues. And NSA analysts have discretion to make those determinations.

This latest leak comes just days after a number of top ranking intelligence officials defended the surveillance program before lawmakers. General Alexander, the head of the NSA, gave voice to what many are wondering about former NSA contractor Edward Snowden.

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ALEXANDER: How was this 29-year-old systems administrator able to access such highly classified information and about such sensitive matters?

TEMPLE-RASTON: And there's another question: how many more documents does Snowden have? Dina Temple-Raston, NPR News. Transcript provided by NPR, Copyright NPR.